A major problem associated with the earth resources monitoring programs is the enormous amount of data that is collected by the monitoring instruments and transmitted to earth from the remote sensor platforms. The quantity of the data is such that its timely analysis is a severe problem, a problem that will be compounded as more sophisticated, higher resolution sensors are employed. If we consider systems having as their purpose feature identification by means of the intensity or ratio of intensities of reflected solar radiation in a number of wavelength bands, then there are a number of approaches to cutting down the data load which might be considered. One obvious approach is to halt data transmission if it is determined that data are uninteresting. Thus, a device that recognizes the presence of excessive cloud cover can signal a halt to data transmission. Similarly, a device that recognizes clear sea water can be used to interrupt data transmission if only departures from clear water are sought.
A more sophisticated function than the editing function described above is that of remote feature identification in real time. If this is accomplished then feature identification rather than raw multispectral data can be transmitted, and an enormous reduction is achieved in the time between data acquisition and utilization.
A typical embodiment of the present invention comprises an integrated optical data preprocessor for multispectral data. The device compares received analog signals in 16 channels with a large set of prerecorded data sets in real time, and classifies the received data on the basis of the comparison. The operating principles of the device are discussed herein, and details of the prototype design are provided along with a discussion of the reasons for the design choices that were made. The prototype is a 16-channel integrated optical data processor utilizing optical subtraction techniques to take a "vector difference" of two sets of analog voltages. It includes a set of 16 signal electrodes and a set of 16 reference electrodes as well as electrodes for trimming the phase of the reference beam.